Method and apparatus for recording and playing back monitored video data

ABSTRACT

A method and an apparatus for recording and playing back monitored video data for recording monitored video data generated continuously for a long time on a magnetic tape, with less S/N degradation by shortening the operation time of the VTR to suppress the degradation of the magnetic tape, recording head, and other mechanical items, wherein video signals from a video camera are converted to digital signals in an A/D converter, compressed and encoded in a compression encoder &amp; decoder circuit, then transferred to a time axis compression circuit including the first memory, the second memory, an SCSI controller, and a hard disk unit, thereafter compressed on the time axis and recorded on the magnetic tape loaded in a D-VHS standard VTR via an I/F circuit. Compressing the video data from the compression encoder &amp; decoder circuit on the time axis in the time axis compression circuit makes shorter the recording time of the video data on the magnetic tape than the actual recording time of the video camera, whereby the VTR is only required to record video data intermittently on the magnetic tape and that a general home VTR can be adopted as the above VTR, moreover the magnetic tape itself is prevented from damages.

This application is a continuation of application Ser. No. 09/780,429,filed Feb. 12, 2001, now issued as U.S. Pat. No. 6,684,024, which is acontinuation of application Ser. No. 09/015,344, filed Jan. 29, 1998,now abandoned. Each application claims the priority of Japaneseapplication Number 9-015190, the disclosure of which is expresslyincorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention relates to methods and apparatuses for recordingand playing back video data, more particularly to a method and anapparatus for recording and playing back monitored video data, whichwill be suitable for recording video data for a long time for thepurpose of monitoring and preventing of crimes.

There is provided a prior art time lapse VTR used as a video datarecording device for recording video data from, a video camera, suitablefor monitoring and preventing crimes. Many of this type VTR are improvedfrom a home VHS VTR which is very popular at present to enable a longtime recording. For example, in such a time lapse VTR, the magnetic tapecan be fed at a ⅓ speed of the VHS Extended Play (EP) mode to recordonly one of the input video 3 fields on the tape, so that the recordingtime can be extended to 3 times that of the EP mode. Consequently, whena 120-min tape is used, the recording time is extended to 6 hours (120min×3) in the VHS EP mode. The recording time of the above time lapseVTR can thus be extended to 18 hours, 3 times that of the VHS EP mode.In this case, however, as understood clearly from the recordingprinciple explained above, the number of fields per second is 20, whichis ⅓ of the VHS (60 fields). In addition, audio signals can be recordedon audio tracks arranged in the longitudinal direction of the tape justlike an ordinary VTR, but the tape speed becomes ⅓ of the normal one. Asa result, the sound quality is degraded more than the normal one. Inspite of this, the time lapse VTR can have an advantage of 18-hour audiorecording time.

There is also proposed an intermittent recording system for the aboveprior art time lapse VTR, in which system, the average tape speed isdelayed and the number of recording fields is reduced more to extend therecording time. This system can have the maximum recording time of, forexample 720 hours using a normal 120-min tape by, recording video dataat a rate of 1 field per 2 seconds (120 fields) per frame (2 hours×3times×120=720 hours). In such a super-long time recording operation, theaverage tape feed speed is very slow, so that it becomes difficult tocontrol the continuous feeding of the tape. To avoid this problem, thetape is fed intermittently in most cases and accordingly, it becomesimpossible to record audio signals in audio tracks.

The conventional time lapse VTR ware opened in, for example, ExaminedPublished Japanese Patent Application No.3-12380, Examined PublishedJapanese Patent Application No.7-63182, etc. The former patent reportdescribes a method for controlling tape feeding so as to obtain the samerecording tape pattern as that of the ordinary VTR even at the recordingtime by feeding the tape intermittently just like in the above-mentioned720-hour recording. The latter patent report (No.7-63182) describes amethod for controlling the rotation speed of the cylinder to preventgeneration of skew during the intermittent recording.

As explained above, the time lapse VTR needs recording modes forcontinuous low speed tape feeding and intermittent tape feeding inaddition to the normal continuous tape feeding, and a means forprecision controlling of the capstan and the cylinder corresponding tothose playback modes. In a recording operation, the same playback modeas each of those recording modes is needed to check pictures at the samespeed as that of the recording. For this purpose, each of those priorart VTRs must be provided with various precision control means, so theirprices become more higher than general home VTRs.

The time lapse art VTR cannot load (wind a magnetic tape onto thecylinder to which a magnetic head is attached to prepare for recordingor playing back) a magnetic tape (video data recording medium) andunload (separate the tape from the cylinder) the magnetic tape within ashort time even for a recording operation in a recording mode forintermittent tape feeding. Therefore, the tape is needed to be keptloaded during recording. Further, since the cylinder has a large momentand takes much time until its rotation speed is stabilized, the cylindermust be rotated almost at a fixed speed continuously during therecording.

Therefore, the time lapse VTR must be kept loaded with a tape duringrecording of monitored video data and the cylinder is rotatedcontinuously. Especially, in the above super-long recording mode(720-hour mode), the VTR has a disadvantage that because the cylinder iskept rotated in contact with the tape for 720 hours, the tape is damagedfar more rapidly than used for a home VTR. In the same way, because thehead is in contact with the tape, the head is also worn rapidly. Themechanisms such as the motor and belt used for making the cylinderrotate are also degraded rapidly and often damaged, since they arerunning for a long time respectively.

Further, conventional helical scanning VTR also has a following defect;the recording track pattern angle on the tape loaded is decided by boththe rotation speed of the cylinder and the feed speed of the tape, sothat the track pattern recorded at the above slow speed tape feeding orthe tape stops has an angle different from the normal speed tapefeeding. Therefore, when playing back the track pattern recorded in suchway, a mismatching occurs between the tracing angle of the head and theangle of the track pattern, causing the SIN (signal-noise ratio) to bedegraded in a part of the playback signals, with the resultant oflowering the quality of output pictures significantly.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method and anapparatus for recording and playing back monitored video data, which canstore video data on a magnetic tape for a period enough to be used formonitoring and preventing crimes, etc. In addition, in the apparatus, itis no need to record video data while the recording head is put incontact with the magnetic tape for a long time and while the recordinghead is moved, without special mechanisms for intermittent feeding, etc.In other words, a general home VTR can also be used to store video dataon a magnetic tape for a period enough to monitor and prevent crimes,etc.

It is another object of the present invention to solve theabove-mentioned problems of conventional time lapse VTR and provide anapparatus for recording and playing back video data, which can improveits mechanical reliability and extend the life of the magnetic tape inuse by reducing the operating time of the parts that will apt to wearand be damaged, without employing any high precision control means forintermittent tape feeding.

It is a further object of the present invention to provide an apparatusfor recording and playing back video data, which can output good qualityplayback images without degrading the playback signals even in adifferent tape-speed mode from the recording mode.

In order to achieve the above objects, according to the presentinvention, video data compressed on the time axis is stored on amagnetic tape, so that when video signals from a monitoring video cameraare to be stored on the magnetic tape continuously for a long time, themagnetic tape recording apparatus is operated for a period shorter thanthe monitoring period. Thus, it is not required to operate the magnetictape recording device (VTR) continuously during the monitoring.

In other words, the present invention provides a method for recordingand playing back monitored video data for storing video signalsgenerated continuously for a long time, on a magnetic tape, whereinwhile continuously generating video signals for a long time and enteringsuch video signals and compressing it on the time axis, then beingoutput as digital video data and recorded on a magnetic tape, so thatthe digital video signals are stored on the magnetic tape for a periodshorter than the period in which the video signals are generatedcontinuously.

Furthermore, the present invention provides an apparatus for recordingand playing back monitored video data and storing video signalsgenerated continuously for a long time on a magnetic tape, comprising ameans of generating video signals continuously for a long time; a meansof entering video signals generated by the video signal generating meanscontinuously for a long time and compressing the video signals on thetime axis so as to be output as digital signal video data; and a meansof recording and playing back digital video data from the time axiscompressing means on a magnetic tape, wherein the period in which themagnetic tape recording means records digital video data on the magnetictape is shorter than the period in which the video signal generatingmeans generates video signals continuously.

In order to achieve the above objects, the monitored data recording &playback apparatus provided by the present invention for recording videoinformation for a long time, comprises the first memory means of storingvideo data temporarily; the first recording & playback means ofrecording the data output from the first memory means on a recordingmedium; the second memory means of storing playback data from the firstrecording & playback means temporarily; the second recording & playbackmeans of recording data output from the second memory means on amagnetic tape by forming oblique tracks on the magnetic tape; and acontrol means of controlling the write and read operations of the firstand second means and recording and playback operations of the first andsecond recording & playback means. The control means controls so thatreading from the first memory means and recording by the first recording& playback means are repeated each time the first specified data amountis reached, as well as controls the first recording & playback means andthe second recording & playback means in the first operation mode sothat they stop recording and playback operations respectively until thedata recorded in the first recording & playback means and not playedback yet reaches the second specified data amount, which is greater thanthe first specified data amount. In addition, the control means controlsthe first and second recording & playback means so that when the datarecorded and not played back yet reaches the second specified dataamount, the first recording & playback means time-shares recording andplayback of data until the data of the second specified data amount isplayed back completely. And furthermore, the control means controls sothat the second recording & playback means records the data read by thesecond memory means at a specified transfer rate on a magnetic tape fedcontinuously while forming oblique tracks on the tape and feeding thetape continuously.

Furthermore, in order to achieve the above objects, the recording &playback apparatus provided by the present invention comprises: thefirst memory means of storing video data temporarily; the first andsecond recording & playback means of recording the data output from thefirst memory means on a recording medium; the second memory means ofstoring playback data from the first and second recording & playbackmeans; the third recording & playback means of recording the data outputfrom the second memory means on a magnetic tape by forming obliquetracks on the tape; and a control means of controlling write and readoperations of the first and second memory means and recording andplayback operations of the first, second, and third recording & playbackmeans, so that when in recording of video data, the control meanscontrols so that four operation modes are changed appropriately asfollows according to the data amount to read and the data amount to playback in the first and second recording & playback means; in the firstoperation mode, the control means controls so that reading of video datafrom the first memory means and recording by the first recording &playback means are repeated each time the first specified data amount isreached and recording and playback operations of the second and thirdrecording & playback means are stopped. In the second operation mode,the control means controls so that reading of video data from the firstmemory means and recording by the second recording & playback means arerepeated each time the first specifier data amount is reached and thevideo data read from the first recording & playback means is stored inthe second memory means temporarily, and then video data is read fromthe second memory means at a specified transfer rate while the thirdrecording & playback means is enabled to record transferred data on themagnetic tape by forming oblique tracks on the tape. In the thirdoperation mode, the control means controls so that reading of video datafrom the first memory means and recording by the second recording &playback means are repeated each time the first specified data amount isreached while recording and playback operations of the first and thirdrecording & playback means are stopped. And, in the fourth operationmode, the control means controls so that reading of video data from thefirst memory means and recording by the first recording & playback meansare repeated each time the first specified data amount is reached, andvideo data read from the second recording & playback means is stored inthe second memory means temporarily, and then video data is read fromthe second memory means at a specified transfer rate while the thirdrecording & playback means is enabled to record transferred data on themagnetic tape fed continuously by forming oblique tracks on the tape.

Furthermore, in order to achieve the above objects, the monitored videodata recording & playback apparatus provided by the present invention,which records compressed and encoded video data on a magnetic tape byforming oblique tracks on the tape, is further provided with a means ofchanging the time order of video data when in a recording operation sothat only the first group video data selected from the above video dataand compressed and encoded in the m (m=an integer of 2 or over) frametime interval is continued by n (n=an integer of 2 or over) frames; ameans of restoring the initial video data time orders of the first groupvideo data and other video data; a means of controlling so as to playback only the first group video data selectively and feed other datafast; and a memory means of storing the played-back first group videodata temporarily.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the monitored video data recording &playback apparatus in the first embodiment o the present invention.

FIG. 2 is a block diagram indicating an example of the configuration ofthe compression encoder & decoder circuit used in the monitored videodata recording & playback apparatus shown in FIG. 1.

FIG. 3 is a block diagram indicating an example of the VTR circuit usedin the monitored video data recording & playback apparatus shown in FIG.1.

FIG. 4 is a block diagram indicating an example of the control circuitused in the monitored video data recording & playback apparatus shown inFIG. 1.

FIG. 5 is a timing chart explaining the operation of the monitored videodata recording & playback apparatus, especially the operation of thecontrol circuit shown in FIG. 1.

FIG. 6 is a block diagram indicating an example of the compressionencoder & decoder circuit used in the monitored video data recording &playback apparatus in the second embodiment of the present invention.

FIG. 7 is a timing chart indicating the operation of the thinning-outcircuit in the second embodiment shown in FIG. 6.

FIG. 8 is a block diagram indicating the configuration of the monitoredvideo data recording & playback apparatus in the third embodiment of thepresent invention.

FIG. 9 is a block diagram indicating an example of the configuration ofthe control circuit used in the monitored video data recording &playback apparatus in the third embodiment.

FIG. 10 is a timing chart indicating the operation of the controlcircuit used in the monitored video data recording & playback apparatusin the third embodiment.

FIG. 11 is a block diagram indicating the configuration of the monitoredvideo data recording & playback apparatus in the fourth embodiment ofthe present invention.

FIG. 12 is a block diagram indicating an example of the configuration ofthe data order change circuit used in the monitored video data recording& playback apparatus shown in FIG. 11.

FIG. 13 is a timing chart indicating the operation of the data orderchange circuit used in the monitored video data recording & playbackapparatus shown in FIG. 11.

FIG. 14 is a timing chart indicating the operation of the monitoredvideo data recording & playback apparatus in the fourth embodiment ofthe present invention shown in FIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereunder, the preferred embodiments of the present invention will beexplained with reference to the attached drawings.

FIG. 1 is a block diagram of the recording & playback apparatus formonitored video data in the first embodiment of the present invention.In FIG. 1, numeral 1 indicates a terminal to input video signals from avideo camera (not illustrated), 2 indicates a terminal to output videosignals, 3 indicates a compression encoder & decoder circuit, 4 and 8indicate semiconductor memories (4: the first memory, 8: the secondmemory), 5 indicates an SCSI (Small Computer System Interface)controller, 7 indicates a hard disk unit (hereafter, to be abbreviatedas HDD) provided with an SCSI interface, 9 indicates a VTR, 10 indicatesa control circuit, 11 indicates an operator panel from which theoperator instructs various operations, 12 indicates an A/D converter, 13indicates a DIA converter, and 14 indicates an IEEE1394 interfacecircuit (hereafter, to be abbreviated as I/F circuit). Of those devices,the semiconductor memories (the first and second memories 4 and 8), theSCSI controller 5, the HDD 7 are combined to form a time axiscompression circuit 100 for compressing video data to record on the timeaxis. Each of those devices forming the circuit 100 will be explainedmore in detail later.

At first, the operation of each device of the recording & playbackapparatus for monitored video data in the above configuration will beexplained. Receiving a recording instruction from the operator panel 11,the control circuit 10 generates control signals needed for eachcorresponding block to record video data. Then, the video signalsentered from a video camera (not illustrated) are supplied to the A/Dconverter 12 via the video input terminal 1. This A/D converter 12converts analog video signals to 8-bit digital signals. After this, thecompression encoder & decoder circuit 3 encodes the digital videosignals supplied from the A/D converter 12 according to the MPEG (MovingPicture Experts Group) standard. Furthermore, the first memory 4, whichis an FIFO (First In First Out) memory being capable of both writing andreading simultaneously, writes and reads MPEG data sequentiallyaccording to the control signals from the control circuit 10.

The SCSI controller 5 sends an SCSI command, which writes MPEG data readfrom the first memory 4 into the HDD 7 according to the control signalsfrom the control circuit 10, to the HDD 7. The HDD 7 provided with anSCSI interface reads the command received from the SCSI controller 5 andwrites the MPEG data entered into itself 7 according to the command. Inaddition, at a timing to be explained later, the SCSI controller 5generates an SCSI command to instruct the HDD 7 to play back necessarydata according to the control signals from the control circuit 10.According to this command, the data output from the HDD 7 is sent to thesecond memory 8.

Just like the first memory 4, the second memory 8 is also an FIFO memorythat can write and read data simultaneously. The second memory 8 thuswrites and reads data sent from the SCSI controller 5 sequentiallyaccording to the control signals from the control circuit 10. Inaddition, the I/F circuit 14 combines the VTR command sent from thecontrol circuit 10 and the MPEG data output from the second memory 8according to the IEEE1394 standard to generate serial data to be sent tothe VTR 9. The VTR 9 then separates this serial data to commands anddata, and writes the separated data on a magnetic tape according to theseparated command. In the monitored video data recording & playbackapparatus, video data from a video camera is recorded on a magnetic tapeloaded in the VTR 9 via the first memory 4, the, HDD 7, and the secondmemory 8 in such way.

Subsequently, the compression encoder & decoder circuit 3 will beexplained. FIG. 2 is a block diagram indicating the configuration of thecompression encoder & decoder circuit 3. In FIG. 2, numeral 21 indicatesa video decoder circuit, 22 indicates a temporal recording circuit, 23indicates a subtraction circuit, 24 and 34 indicate switches, 25indicates a DCT (Discrete Cosine Transform) circuit, 26 indicates aquantizer circuit, 27 indicates a variable length encoder circuit, 28and 35 indicate data buffers, 29 and 37 indicate inverse quantizercircuits, 30 and 38 indicate inverse DCT circuits, 31 and 39 indicateadder circuits, 32 and 41 indicate image memories, 33 indicates a motioncompensation prediction circuit, 36 indicates a variable length decodercircuit, 40 indicates a motion compensation circuit, 42 indicates avideo encoder circuit, 43 indicates a freeze control circuit, and 44indicates a switch.

In the compression encoder & decoder circuit 3 having such aconfiguration, video signals digitalized in the A/D converter 12 areconverted by the video decoder circuit 21 to luminance signals and colordifference signals according to the number of pixels needed forencoding. In the case of the MPEG's B (Bidirectionally predictive-coded)pictures, video data whose timings are reversed are used for encoding,so input video data are reordered in the temporal reordering circuit 22according to each picture type of I (Intra-coded), B, and P(Predictive-coded). In addition, input image data and difference dataare selected in the switch 24 corresponding to the intra-frame encodingand The inter-frame encoding. Furthermore, selected image data isconverted to a spatial frequency region in units of a block comprising 8pixels×8 lines in the DCT circuits 25. The data is then quantized in thequantizer circuit 26 through an operation with a quantization matrix.This quantized data is encoded to variable length data in the variablelength encoder circuit 27 together with the motion vector from themotion compensation prediction circuit 33 and encoded mode information.The data is then stored in the buffer 28 until it is output as MPEG bitstreams.

The buffer 28 outputs the amount information of the data stored in thebuffer to the control circuit 10, so that the buffer is prevented fromboth overflow and underflow. On the other hand, the quantized data isdecoded locally by the inverse quantizer circuit 29 and the inverse DCTcircuit 30, then stored in the image memory 32. The switch 34 is changedover corresponding to the intra-frame encoding and the inter-frameencoding. Furthermore, the decoding motion compensation predictioncircuit 33 decides an encoding mode and detects a motion vectoraccording to the image data from the image memory 32 and input imagedata. The circuit 33 also generates and outputs reference image dataneeded for inter-frame encoding and inter-frame decoding.

On the contrary, when in a playback operation, data is decoded byfollowing the above recording processings in reverse. In other words,each bit stream from the first memory 4 is stored in the buffer 35first, then the parameters of the bit stream such as encoding mode,motion vector, etc. are separated in the variable length decodingcircuit 36. After this, the data is restored to image data in theinverse quantizer circuit 37 and the inverse DCT circuit 38. Inaddition, in the motion compensation prediction mode, block data whosemotion compensation is predicted is added to the data in each of theimage memory 41, the motion compensation circuit 40, and the addercircuit 39 respectively, then composite signals are generated and outputfrom the video encoder circuit 42. The switch 44 usually selects the aside. When instructed “Freeze” from external, however, the freezecontrol circuit 43 stops writing into the image memory 41 at a timing atwhich the compression & decoding time is corrected. At the same time,the switch 44 is pushed down to the b side so that data read from theimage memory 41 is entered into the video encoder 42. Thus, a frozenimage can be output.

Subsequently, the details of the VTR 9 shown in FIG. 1 will be explainedwith reference to Table 1 and FIG. 3.

This VTR 9 conforms to the D-VHS standard so as to be enabled to recordand playback digital signals on the basis of the VHS mechanical system.Table 1 shows the basic technical specifications of this D-VHS standard(STD) mode.

TABLE 1 Tape Newly established grade based on S-VHS tape Cassette D-VHScassette Mechanism Based on present VHS mechanism RecordingTime/Capacity Standard . . . DF-300 (5 hours, 31.7 GB) Max . . . DF-420(7 hours, 44.4 GB) Track Composition Tape speed 16.67 mm/sec Headazimuth +−30 deg. Drum rotation 1800 rpm Tracking system CTL tracksystem Recording Specification Main data input rate 14.1 Mbps Sub datainput rate 0.146 Mbps Recording rate 19.14 Mbps Track structure 1 sectorLength of sync block 112 bytes Inner ECC RS code Outer ECC RS code Codeword shuffling 6 tracks Modulation system SI-NRZI Interface Based onIEEE1394 digital interface

In other words, the speed of this D-VHS tape (refer to the section oftrack composition) is a half of that of the VHS standard (SP) mode. Whena standard tape is used, main data (video and audio) of 14.1 Mbps (bitper second) can be recorded for 5 hours.

In the block diagram indicating the configuration of the VTR 9 shown inFIG. 3, numeral 71 indicates an IEEE1394 digital interface circuit(hereafter, to be abbreviated as I/F circuit), 72 indicates an errorcorrection encoder, 73 indicates a modulator circuit, 74 indicates acontrol circuit, 75 indicates a servo circuit, 76 indicates an errorcorrection decoder, 77 indicates a demodulator circuit, 78 indicates awave equalizer & selector circuit, 79 indicates a magnetic tape, 80indicates a rotary cylinder, 81 and 82 indicate magnetic heads, and 83indicates a capstan.

In this configuration of the VTR 9, a recording mode command and data torecord are entered into the I/F circuit 71 on the VTR 9 side from theI/F circuit 14 on the HDD 7 side when in a recording operation. Then,the I/F circuit 71 separates the command from the data, and sends thecommand to the control circuit 74 and the data to the error correctionencoder 72 respectively. On the other hand, the control circuit 74 sendsnecessary control signals to each device to instruct the VTR 9 toexecute specified operations according to the entered commands of“RECORD”, “PLAYBACK”, etc. In other words, the error correction encoder72 shuffles data in units of 6 tracks as shown in Table 1, to execute RS(Read Solomon) encoding. After this, the data is modulated to SI-NRZIdata in the modulation circuit 73, then recorded on the magnetic tape 79via the magnetic heads 81 and 82 attached to the rotary cylinder 80. Theservo circuit 75 controls the rotation speed and phase of the rotarycylinder 80 and the capstan 83 to form the specified tracks on themagnetic tape 79.

On the contrary, receiving the “PLAYBACK” command via the I/F circuit71, the control circuit 74 sends control signals necessary for aplayback operation to each device. When in such a playback operation,data on the magnetic tape 79 is played back by the magnetic heads 81 and82 and entered into the wave form equalizer & selector 78. This waveformequalizer & selector 78 integrates and equalizes data to compensate thedifferential characteristics by magnetic recording & playback operation,then decides “1” or “0” by comparing the result with the thresholdlevel. In addition, the demodulator circuit 77 executes a reverseprocessing of the processing of the modulator circuit 73. Then, theerror correction decoder 76 corrects errors generated in arecording/playback process and to restore the data order throughdeshuffling. And, the data from the error correction demodulator 76 isoutput via the I/F circuit 71.

Receiving the “STOP” command via the I/F circuit 71, the control circuit74 sends control signals to the servo circuit 75 to stop the rotarycylinder 80 and the capstan 83, as well as unloads the magnetic tape 79(separates the magnetic tape79 from the rotary cylinder 80).

Subsequently, the operation of the control circuit 10 will be explained,especially focusing on the recording operation, with reference to FIG.4. FIG. 4 is a block diagram indicating the configuration of the controlcircuit 10 when in a recording operation. In FIG. 4, numeral 51indicates the first memory write control circuit, 52 indicates the firstmemory read control circuit, 53 indicates the first memory data amountmonitoring circuit, 54 indicates an HDD recording control circuit, 55indicates a mode decision circuit, 56 indicates an HDD playback controlcircuit, 57 indicates an HDD data amount monitoring circuit, 58 is thesecond memory write control circuit, 59 indicates the second memory readcontrol circuit, and 60 indicates the second memory data amountmonitoring circuit. 24

In the control circuit 10 having such a configuration, the first memorywrite control circuit 51 sends control signals to the first memory 4when data is to be recorded. According to the control signals, thememory 4 writes data in itself 4. At this time, the first memory writecontrol circuit 51 controls the average write frequency of the firstmemory 4 according to the data amount information from the buffer 28 ofthe compression encoder & decoder 3 to prevent the buffer 28 from bothoverflow and underflow. This operation can be realized by controllingthe buffer so that, for example, data is written in the buffer 28 at afrequency higher than the average write frequency and writing is stoppedtemporarily when the data count in the buffer 28 comes close to zero. Inaddition, the first memory read control circuit 52 sends control signalsto the first memory 4 according to the mode signal from the modedecision circuit 55, thus reading the data from the first memory.

The first memory data amount monitoring circuit 53 in the controlcircuit 10 incorporates a counter circuit used for monitoring thedifference between the amount of the bit stream data stored in the firstmemory 4 and the amount of the data read from the memory 4. The circuit53 generates an MRR1 (Mmeory 1 Read Request) signal according to thecount value and sends the signal to the mode decision circuit 55. ThisMRR1 signal is used for preventing the first memory 4 from overflow. Forexample, the first memory 4 is set to the low level until the countervalue reaches the specified value (eg., 15.5 Mbits) and to the highlevel when the value is exceeded, keeping the level high until the countvalue reaches a value close to zero (eg., 0.5 Mbits) or under.

The HDD recording control circuit 54 and the HDD playback controlcircuit 56 provided in the control circuit 10 respectively generatecontrol signals necessary for recording and playing back data in andfrom the HDD 7 according to the commands from the mode decision circuit55 and send the control signals to the SCSI controller 5. In otherwords, the HDD recording control circuit 54 increases the write addressfrom zero sequentially and controls so that the maximum value isreturned to zero cyclically. The HDD playback circuit 56 also controlswrite addresses just like the circuit 54. As a result, the hard diskunit (HDD) 7 works as a means of recording and playing back datacyclically, that is, as an FIFO (First In First Out). The HDD dataamount monitoring circuit 57, when in recording, incorporates a counterused for monitoring the difference between the amount of the recordeddata in the hard disk unit (HDD) 7 and the amount of the data read(played back) from the HDD 7. The HDD data amount monitoring circuit 57generates an HRR (Hard Disk Read Request) signal according to thiscounter value and sends the signal to the mode decision circuit 55. Inother words, this HRR signal prevents the HDD 7 from overflow. Forexample, the HDD 7 is set to the low level until the counter valuereaches the second specified amount (eg., 1 GB), and the HDD 7 is sea tothe high level when the counter value exceeds the second specifiedamount, keeping the level high until the counter value reaches a valueclose to zero (eq., 0.5 Mbits) or under.

Furthermore, the second memory write control circuit 58 and the secondmemory read control circuit 59 generate control signals necessary for awrite/read operation in/from the second memory according to the commandsfrom the mode decision circuit 55 and sends the signals to the secondmemory 8. On the other hand, the second memory data amount monitoringcircuit 60 incorporates a counter circuit used for monitoring thedifference between the amount of the bit stream data written in thesecond memory 8 and the amount of the data read from the memory 8. Thesecond memory data amount monitoring circuit 60 generates an MWR2(Memory 2 Write Request) signal and an MRR2 (Memory 2 Read Requestsignal according to the counter value and sends those signals to themode decision circuit 55. This MWR2 signal requests that data is to beentered into the second memory 8 when data in the memory 8 becomes less.For example, the second memory 8 is set to the high level when thecounter value reaches a ¼ capacity (4 M bits) of the full memorycapacity (eg., 16 M bits), keeping the level high until the countervalue reaches ¾ (12 M bits) of the second memory capacity (16 M bits) orover. When the counter value becomes ¾ or over, the memory 8 is set tothe low level again. The MRR2 signal indicates that enough data iswritten in the second memory 8, so that data can be read from the memory8 at a certain rate. For example, when the counter value reaches ½ ofthe second memory 8 capacity (16 M bits) or over, the memory 8 is set tothe high level, keeping the level high until the counter value reacheszero. When the counter value reaches zero, the memory 8 is set to thelow level.

The mode decision circuit 55 provided in the control circuit 10 decidesan operation mode according to the MRR1 signal, the HRR signal, the MWR2signal, and the MRR2 signal and sends commands to the first memory readcontrol circuit 52, the HDD recording control circuit 54, the HDDplayback control circuit 56, the second memory read control circuit 59and the I/F circuit 14 so that those devices operate corresponding tothe decided mode. Table 2 shows the relationships among input signals,output commands, and selected modes.

In Table 2, “-” indicates “Don't Care”. When the “STOP” command isissued, the mode decision circuit 55 sends the “STOP” command to each ofthe above devices. Consequently, the first memory 4 stops reading, theHDD 7 stops recording/playback, the second memory 8 stopswriting/reading, and the VTR9 stops recording.

When the “HDD RECORD” command is output, the mode decision circuit 55sends the command to both the first memory read control circuit 52 andthe HDD recording control circuit 54 to execute the specified operation.As a result, data is read from the first memory and the data is thenwritten in a hard disk provided in the HDD 7 via the SCSI controller 5.

When the “HDD PLAYBACK” command is output, the mode decision circuit 55sends the command to both the HDD playback control circuit 56 and thesecond memory write control circuit 58 to execute the specifiedoperation. As a result, data is read from the hard disk provided in theHDD 7 and the data is written in the second memory via the SCSIcontroller 5.

TABLE 2 Operation Mode MRR1 HRR MWR2 MRR2 Command Output Selected Mode1st Mode L L — — STOP H — — — HDD RECORD L H — — STOP To 2nd mode 2ndMode L H L L STOP H — — — HDD RECORD L H H — HDD READ — — — H VTR RECORDL L L L STOP To 1st mode

Furthermore, when the “VTR RECORD” is output, the mode decision circuit55 sends the command to both the second memory read control circuit 59and the I/F circuit 14 to execute the specified operation. As a result,data is read from the second memory and the data is then recorded on themagnetic tape loaded in the VTR 9 via the I/F circuit 14.

Subsequently, a long video recording operation of the recording &playback apparatus will be explained sequentially with reference to thetiming chart shown in FIG. 5. The details of the apparatus configurationis as explained above. (The above recording operation means an operationfor compressing video data on the time axis in the time axis compressingcircuit 100 mentioned above.)

At first, when the apparatus begins a recording operation, data iswritten almost continuously in the first memory 4. (In this chart,however, the above-mentioned temporary write stop period is notdescribed to simplify this “first memory write” signal waveform.)

After a period of time T1, the data amount in the first memory 4 reachesthe first specified value (15.5 M bits) and the MRR1 signal thatrequests data reading from the first memory 4 is set to the high level.Consequently, data is read from the first memory 4 and the data isrecorded in the HDD 7 only for the next period of time T2. In otherwords, data is kept read from the first memory 4 until the data amountin the memory 4 reaches 0.5 M bits. This means that about 15 M bits ofdata from this first memory 4 is recorded in the HDD 7. After this,reading from the first memory 4 and recording into the HDD 7 areexecuted intermittently in the same way.

Hereunder, the times of both T1 and T2 are calculated approximately tounderstand how the above operations are executed actually.

If the average data rate of the bit stream output from the compressionencoder/decoder circuit 3 is assumed to be R1 (eg., R1=1.5 M bps), thetime T1 required until the data amount in the first memory 4 reaches thefirst specified value D1 (D1=15.5 M bits) from zero (0) is calculated asfollows.T1=D1/R1=15.5 M bits/1.5 M bps=10.3 sec

On the other hand, if the average recording/playback data rate of theHDD 7 is assumed to be R2 (eg., R2=30 M bps), the time T2 required forrecording the data amount obtained by subtracting 0.5 M bits from thefirst specified value D1 (D1 (=15.5 M bits)−0.5 M bits=15 M bits) iscalculated as follows.T2=(D1−0.5)/(R2−R1)=15 M bits/(30−1.5)M bps≈0.5 sec

Consequently, in the above operation mode, that is, in the firstoperation mode, the HDD 7 stops for about 10 sec after it begins anoperation. Then, the HDD 7 records data only for about 0.5 sec. The HDD7 repeats the operation cyclically.

After data transfer from the first memory 4 to the HDD 7 is repeatedsuch way, the data amount in the HDD 7 increases. When the secondspecified value (eg., 1 GB) is reached, for example, the HRR signal(refer to the 57 shown in FIG. 4) requesting data reading from the HDD 7is set to the high level. And, after this, the apparatus enters thesecond operation mode. Since the data amount in the second memory 8 iszero (0) just after this second operation mode is entered, the MWR2signal (refer to the 60 shown in FIG. 4) requesting the second memory toread data is set still in the high level. Thus, the HDD 7 outputs dataand data is written in the second memory 8. And accordingly, the data inthe HDD 7 is written in the second memory 8 via the SCSI controller 5.The average output data rate of the HDD 7 is assumed to be 30 M bps justlike in the above recording operation at this time.

The data amount in the second memory 8 increases due to this writingfrom the HDD 7. After this, when the data amount in the second memory 8reaches 8 M bits, the MRR2 signal requesting reading from the secondmemory 8 is set to the high level, and accordingly, data is read fromthe second memory 8 and the VTR9 records the data. The reading data rateof the second memory 8 and the input data rate of the VTR 9 are setequally (14.1 M bps). This fixed rate data is recorded on the magnetictape 79 loaded in the VTR 9 from the second memory 8 via the I/F circuit14. The VTR 9 feeds the magnetic tape 79 continuously at a fixed rate(16.67 mm/sec) at this time. In other words, the VTR 9 is operated inthe normal recording mode.

When the data amount in the second memory 8 reaches 12 M bits, the MWR2signal requesting writing into the second memory 8 is set to the lowlevel. Thus, the HDD 7 stops the output and the writing into the secondmemory 8 is also stopped. Reading from the second memory 8 and recordinginto the VTR 9 are continued on even during this period, however. So,the data amount in this second memory 8 is reduced little by little.

After this, when the data amount in this second memory 8 is reduced to 8M bits, the MWR2 signal requesting writing into the second memory 8 isreturned to the high level. And accordingly, data outputting from theHDD 7 and writing into the second memory are restarted. The data amountin the second memory 8 begins increasing again. As understood clearlyfrom the waveform shown in the chart(especially, refer to the HDD OUTPUTsignal), writing/reading in/from the HDD 7 is controlled so as to betime-shared.

Hereafter, the same operations are repeated, so the data amount in theHDD 7 decreases. When the data amount in the HDD 7 is reduced to 0.5 Mbits or under, the HRR signal requesting reading from the HDD 7 is setto the low level. After this, however, reading from the second memory 8and recording into the VTR 9 are continued until the data in the secondmemory is read completely. When the data amount in the second memory 8reaches zero (0), the MWR2 signal is set to the high level and the MRR2signal is set to the low level. Thus, the second operation mode isexited. In other words, the first operation mode is set again.

In the monitored video data recording & playback apparatus of thepresent invention, data is compressed on the time axis and the first andsecond operation modes are alternated as explained above when inrecording and this operation is continued until the magnetic taperecording the data reaches the end of the tape.

Subsequently, the video recording time of the monitored video datarecording & playback apparatus of the present invention and the VTRrecording time to be reduced by the time axis compression will beexplained.

If the capacity of one magnetic tape is assumed to be D3 (D3=31.7 GB forthe standard tape as shown in Table 1), the possible recording time T3is represented as follows.T3=D3/R1=31.7 GB/1.5 M bps=(31.7×8×1000)M bits/1.5 M bps≈169067 sec≈47hours

In other words, one magnetic tape can record data for about 47 hours.

However, since the total recording time T4 of the VTR 9 is obtained bydividing the magnetic tape capacity (D3) by the main data input rate(R3) shown in Table 1, the result becomes as shown below.T4=D3/R3=31.7 GB/14.1 M bps=31.7×8×1000)M bits/14.1 M bits≈17986≈300min=5 hours

The periods of the first and second operation modes (first operationmode: τ1, second operation mode: τ2) when in a recording operation areas shown below.

At first, since the first operation mode period τ1 means a time requireduntil the amount of the image data output from the compression encoder &decoder circuit 3 (bit stream average data rate=1.5 M bps) is stored inthe HDD 7 and the data amount reaches the second specified value (eg., 1GB) from the minimum value of 0.5 M bits, it is calculated as follows.τ1=(1 GB−0.5 M bits)/R1=(8×1000−0.5)M bits/1.5 M bps=5333 sec≈89 min≈1hour 29 min

On the other hand, since the second operation mode period τ2 means atime required until the data in the HDD 7 that reaches the secondspecified value is recorded on the magnetic tape 79 loaded in the VTR 9(input data rate=14.1 M bps), then the data amount reaches the minimumvalue of 0.5 M bits (1 GB−0.5 M bits), it is calculated as follows.τ2=(1 GB−0.5 M bits)/R2=(8×1000−0.5)M bits/14.1 M bps=567 sec≈9 min 27sec

Consequently, after stopping for about one and half hours (in the firstoperation mode) on the standard magnetic tape (=31.7 GB) in the aboveapparatus due to the compressing operation executed by the time axiscompression circuit 100 on the video data time axis, the D-VHS standardVTR 9 records data only for about 10 min (in the second operation mode).Repeating this cycle operation, the VTR 9 can record about 47-hour videodata in an operation of about 5 hours. (This means that both the timewhen the magnetic tape 79 is in contact with the heads 81 and 82 and thetime when the magnetic tape 79 is in contact with the rotary cylinder 80while they are running are 5/47 of those of the conventional time lapseVTR respectively.) The conditions of this operation are not strict somuch when compared with those of ordinary home VTRs. Consequently, ageneral home D-VHS standard VTR can be used as the VTR 9 without takingany special measures for that. The magnetic tape can also be protectedfrom damages, since it is not kept loaded and not in contact with thecapstan and the recording head for a long time. In other words,according to the present invention, the D-VHS standard VTR 9 used torecord video data on a magnetic tape does not need any long timecontinuous recording, which is assumed as a special condition for amonitoring purpose, so a low-price home VTR can be used as the VTR 9. Inaddition, the failure rate is very low and the magnetic tape used forthe apparatus can be protected from damages and wear. In the VTR 9 inhis embodiment, the magnetic tape 79 is unloaded when the VTR 9 stops.However, the rotary cylinder may be stopped when the CTR 9 stops only toloosen the tension of the magnetic tape. Even in such a case, since thefriction among the magnetic tape, the rotary cylinder, and the magnetichead is almost eliminated while the VTR 9 stops, the same effect as theabove can be obtained.

On the other hand, the playback operation of the apparatus of thepresent invention will be as follows. The VTR 9 feeds the magnetic tapeat the normal continuous feeding rate (16.67 mm/sec) to playback videodata. Consequently, the output data rate of the VTR9 is 14.1 M bps. And,when in a playback operation, data flows reversely from the aboverecording operation; the data played back by the VTR 9 is sent to thecompression encoder & decoder circuit 3 via the I/F circuit 14, thesecond memory 8, the SCSI controller, the HDD 7, and the first memory 4.After this, the data is MPEG-decoded, then converted by the D/Aconverter 13 to analog signals and output from the terminal 2.

Even in this playback operation, each memory and the HDD 7 arecontrolled so as to be prevented from overflow and underflow just likein the recording operation mentioned above. In addition, when in aplayback operation, the transfer rate of the data to be entered into thecompression encoder & decoder circuit 3 is 1.5 M bps just like at therecording time. So, the VTR 9 carries out a normal playback operationonly while the specified amount of data is stored in the HDD 7.Otherwise, the VTR 9 stops. Even while the VTR 9 stops, however, data isread from the HDD 7 and sent to the compression encoder & decodercircuit 3. The flow of output video data is thus never stopped. Themethod to control this playback operation is similar to the aboverecording method, so detailed explanation of the operation timing willbe omitted here. Consequently, the operation time of the VTR 9 forplaying back 47-hour video data that can be recorded on one standardmagnetic tape will also be only about 5 hours in this case.

Subsequently, the monitored video data recording & playback apparatus inthe second embodiment of the present invention will be explained.

In this second embodiment, the input video data time axis is thinned outto record video data at a smaller rate and enable super-long timecontinuous recording of video data.

At first, FIG. 6 is a block diagram of the compression encoder & decodercircuit (refer to 3 in FIG. 1, and FIG. 2) to thin out the above timeaxis. This compression encoder & decoder circuit differs from thecompression encoder & decoder circuit 3 shown in FIG. 2 in that athinning-out circuit 45 is added and the speed of the compressionencoding main processor (enclosed by a broken line) operation can bechanged according to the mode signal from the thinning-out circuit 45.This thinning-out circuit 45 writes the frame period of video data fromthe decoder 21 in a memory and reads the data from the memory for ak-frame period at a reading rate of 1/k (k=a natural number of 2 orover).

FIG. 7 shows the input and output timings of the thinning-out circuit 45when the k value is 3. In this case, the operation speed of thecompression encoding main processor is set to ⅓. Consequently, the inputsignal time axis is thinned out to ⅓, and the compressed and encoded bitstream is output from the buffer at a ⅓ data rate (0.5 M bps when otherconditions such as quantization, etc. are the same as those of the firstembodiment). In addition, one magnetic tape can record data for 141hours, which is three times that of the first embodiment (47 hours).

According to the second embodiment, the output data rate of thecompression encoder & decoder circuit 3 becomes 1/k, so one standardmagnetic tape can record (monitor) k times (47×k hours) when otherconditions such as quantization, etc. are the same as those of the firstembodiment. However, when the recording time of the VTR 9 can becalculated with the above expression, the result becomes 5 hours justlike in the first embodiment. And, the VTR 9 stops for a 1.5×k hours (inthe first operation mode), then records data only for about 10 min (inthe second operation mode) at this time. Consequently, the wear anddamages of the magnetic tape 79, the heads 81 and 82, and the rotarycylinder 80 in the VTR 9, as well as the degradation of the motor, thebelt, and other items can be reduced to 1/k of those of the firstembodiment respectively (when the monitoring/recording time is thesame).

Subsequently, the third embodiment of the present invention will beexplained. FIG. 8 is a block diagram of the monitored video datarecording & playback apparatus in the third embodiment of the presentinvention. In FIG. 8, numeral 15 indicates the second SCSI controller(SCSI controller 2), 16 indicates the second hard disk unit, and 17indicates a control circuit. Other items given the same numerals asthose in FIG. 1 are the same as those in FIG. 1. In the aboveconfiguration, data output from the first memory 4 is recorded in boththe first hard disk unit 7 (hereafter, to be abbreviated as HDD 1) andin the second hard disk unit (hereafter, to be abbreviated as HDD 2)alternately. Data output from the HDD 1 and from the HDD2 alternately iswritten into the second memory 8. Also in this third embodiment, data iswritten/read into/from HDD in any case via the SCSI controller 5 or 15just like in the first embodiment.

FIG. 9 is a block diagram of the control circuit 17 shown in FIG. 8especially in a recording operation. In FIG. 9, numeral 63 indicates anHDD2 recording control circuit, 64 indicates an HDD1 output controlcircuit, 65 indicates an HDD2 output control circuit, 66 indicates anHDD1 internal data amount monitoring circuit, 67 indicates an HDD2 dataamount monitoring circuit, 68 and 69 indicate switches, and 70 indicatesa mode decision circuit. Other items given the same numerals as those inFIG. 6 are the same as those in FIG. 4.

Hereunder, the recording operation of this control circuit 17 will beexplained. At first, the HDD recording control circuits 62 and 63function just like the HDD recording control circuit 54 shown in FIG. 6.The HDD output control circuits 64 and 65 also function just like theHDD output control circuit 56 shown in FIG. 6. In addition, the HDD1data amount monitoring circuit 66 functions just like the HDD dataamount monitoring circuit 57 shown in FIG. 4. In other words, thecircuit 66 generates the HRR1 (Hard Disk 1 Read Request) signal andsends the signal to the mode decision circuit 70. The HDD data amountmonitoring circuit 67 also functions just like the HDD data amountmonitoring circuit 57 shown in FIG. 4. The circuit 67 generates the HRR2(Hard Disk 2 Read Request) signal and sends the signal to the modedecision circuit 70.

The mode decision circuit 70 outputs commands to each device accordingto the MRR1 signal, the HRR1 signal, the HRR2 signal, MWR2 signal, andthe MRR2 signal entered into itself and controls the switches 68 and 69.Table 3 shows the relationships among those input signals, outputcommands, and switch controls.

In other words, the “HDD RECORD” command is sent to the HDD1 or HDD2record control circuit 62 or 63 via the switch 68. The “HDD OUTPUT”command is sent to the HDD1 or HDD2 output control circuit 64 or 65 viathe switch 69.

Subsequently, the operation of the monitored video data recording &playback apparatus whose configuration is explained above will beexplained with reference to the timing chart shown in FIG. 10. Theexplanation will be made mainly for the differences from the firstembodiment, centering on the recording operation.

When a recording operation is started, the first operation mode (thefirst mode in FIG. 10) is set. At this time, the switch 68 selects theHDD1 and the switch 69 selects the HDD2 according to the control signalsfrom the mode decision circuit 70. Consequently, the operation in thisfirst operation mode becomes the same as that in the first operationmode in the first embodiment. Then, the data in the HDD1 increases. Whenthe HRR1 signal is set to the high level, the second operation mode(second mode) is set.

In this second operation mode, the mode decision circuit 70 makes theswitch 68 select the HDD2. As a result, the “HDD RECORD” command isentered into the HDD2 in the second operation mode. And, the data readfrom the first memory 4 is written into the HDD2. On the other hand, theswitch 69 is changed over to select the HDD1. Then, the “HDD OUTPUT”command is entered into the HDD1 in the second operation mode.Consequently, the data output from the HDD1 is written into the secondmemory 8. In other words, in this third embodiment, the output from theHDD1 is always executed according to the MWR2 signal unlike the firstembodiment. Recording into the HDD1 is thus never interrupted by theMRR1 signal. The data amount in the HDD1 decreases due to this outputoperation. When the data amount reaches 0.5 M bits or under, the HRR1signal is set to the low level. After this, the data amount in thesecond memory 8 reaches zero (0), when the MRR2 signal is set to the lowlevel. As a result, the operation enters the third operation mode (3rdmode).

TABLE 3 Operation MWR MRRR Command Mode Mode MRR1 HRR1 HRR2 2 2 OutputSW68 SW69 Change 1st Mode L L — — — STOP HDD1 HDD2 H — — — — HDD RECORDL H — — — STOP To 2nd mode 2nd Mode L H — L L STOP HDD2 HDD1 H H — — —HDD RECORD — H — H — HDD OUTPUT — — — — H VTR RECORD — L — — L STOP To3rd mode 3rd Mode L — L — — STOP HDD2 HDD1 H — — — — HDD RECORD L — H —— STOP To 4th mode 4th Mode L — H L L STOP HDD1 HDD2 H — H — — HDDRECORD — — H H — HDD OUTPUT — — — — H VTR RECORD — — L — L STOP To 1stmode

In this third operation mode, the switches 68 and 69 are set just likein the second operation mode. The data read from the first memory 4 isthus written into the HDD2. This HDD2 does not output any data at thistime. So, the data amount in the HDD2 increases. And, when the HRR2signal enters the high level, the fourth operation mode (4th mode) isset.

In this fourth operation mode, the switches 68 and 69 are set just likein the first operation mode. In this fourth mode, writing and readinginto/from HDD1 and HDD2 are alternated by exchanging the HDD1 and HDD2.In other words, when the data amount in the HDD2 becomes less and theHRR2 signal enters the low level, and then when the data amount in thesecond memory 8 becomes zero (0) and the HRR2 signal enters the lowlevel, the operation mode returns to the first one.

In the monitored video data recording & playback apparatus in the thirdembodiment of the present invention explained above, the output from theHDD 7 or 16 is never interrupted by the MRR1 signal. In other words,recording and output operations are not time-shared. Consequently, thepresent invention can have an advantage for using a hard disk unit whoserecording or output data rate is comparatively low. In other words, whenthe output rate of the compression encoder & decoder circuit 3 is 1.5 Mbps, the recording rate should be 1.5 M bps or over. When the input datarate of the VTR 9 is 14.1 M bps, the playback data rate should be 14.1 Mbps or over. And, just like in the firs embodiment, the wear anddegradation of the magnetic tape 79, the head 81 and 82, and othermechanical parts can be reduced effectively.

Hereunder, another embodiment of the present invention will further beexplained. FIG. 11 is a block diagram of the monitored video datarecording & playback apparatus in the fourth embodiment of the presentinvention. In FIG. 11, numeral 18 indicates a data sorting circuit and19 indicates a control circuit. Other items given the same numerals asthose in FIG. 1 are the same as those in FIG. 1.

FIG. 12 is a block diagram indicating the configuration of the datasorting circuit 18. In FIG. 12, numeral 101 indicates a type judgementcircuit, 102, 103, 109, and 110 indicate FIFO memories, 104 and 111indicate memory control circuits, 105 indicates an order code addingcircuit, 106 and 107 indicate FIFO buffers, 108 indicates a codedecision circuit, 112 and 114 indicate switch circuits, and 113indicates an order code deletion circuit.

In the configuration of the above data sorting circuit 18, the typedecision circuit 101 detects the sync code (Picture Start Code to beabbreviated as PST) and the video type code (Picture Coding Type to beabbreviated as PCT) for starting a picture layer from the MPEG bitstream output from the compression encoder & decoder circuit 3 when in arecording operation to decide the video type (I picture, P picture, or Bpicture) and sends the information to the memory control circuit 104 andthe order code adding circuit 105. The order code adding circuit 105adds an order code to each picture. This order code indicates the orderof each picture layer in the MPEG bit stream. For example, the ordercode is generated in the counter circuit counting up each time a PST isdetected. The memory control circuit 104 receives the data amountinformation of the buffer 28 output from the compression encoder &decoder circuit 3 through the control circuit 19 and generates controlsignals for writing data into the memories 102 and 103 according to theinformation (so as to prevent the buffer 28 from overflow andunderflow). At this time, P and B picture data are controlled so as tobe written into the PB memory 103 according to the video typeinformation output from the type judgement circuit 101. Other data, thatis, various sync codes and the data such as the number of pixels, thenumber of lines, etc. in the video sequence layer, as well as I pictureare written into the I picture memory 102. Furthermore, the memorycontrol circuit 104 counts the data amount of both P and B picturesusing entered video type information. The circuit 104 resets the countvalue when the specified value is reached (eg., 600 tracks on themagnetic tape). The circuit 104 then generates control signals so thatthe data having been written into the I memory 102 so far is read andtransferred to the buffer 106 via the switch 114. After this, thecircuit 104 generates control signals so that the data written into thePB memory 103 is read during the above same period and transferred tothe buffer 106 via the switch 114.

FIG. 13 is a timing chart of the data sorting circuit 18 when in arecording operation. As understood clearly from this chart, writing andreading into/from the I memory 102 and the PB memory 103 are controlledas explained above to obtain the output bit stream as shown at thebottom in FIG. 13. In other words, I picture data (including varioussync codes and data such as the number of pixels, the number of lines,etc. in the video sequence layer) is output first, then P and B picturedata for 600 tracks is output. FIG. 13 shows data output (P and Bpictures for 600 tracks) only by once, but the operation is repeatedactually to output a bit stream comprising only an I picture and a bitstream comprising P and B pictures are output alternately.

The bit stream shown in FIG. 13 and output from the data sorting circuit18 is transferred to the VTR 9 via the first memory 4, the SCSIcontroller 5, the HDD 7, the second memory 8, and the I/F circuit 14just like in the first embodiment, so that the data is recorded on themagnetic tape 79. As for the track pattern on the magnetic tape 79, asection recording only an I picture and a section recording P and Bpictures are alternated. Thus, 600 tracks are recorded with P and Bpictures.

In the monitored video data recording & playback apparatus in thisfourth embodiment, the data played back by the VTR 9 is entered into thedata sorting circuit 18 via the I/F circuit 14, the second memory 8, theSCSI controller 5, the HDD 7, and the first memory 4 when in a normalplayback operation. This entered playback data is then entered into boththe order code deletion circuit 113 and the code judgement circuit 108via the buffer 107. The code decision circuit 108 detects the PCT(Picture Coding Type) and the order code added in the order codeaddition circuit 105 when in a recording operation and sends bothinformation items to the memory control circuit 111 and the order codedeletion circuit 113. This order code deletion circuit 113 deletes theorder code from the playback data using the order code timinginformation output from the code judgement circuit 108. The memorycontrol circuit 111 generates control signals according to the videotype (I, P, and B pictures information from the code judgement circuit108 so that P picture data is written into the I memory 109 and P and Bpicture data is written into the PB memory 110. The memory controlcircuit 111 generates control signals according to the order indicatedby the order code output from the code judgement circuit 108 so thatdata is read from the I memory 109 and the PB memory 110. This read datais then output via the switch 112 and sent to the compression encoder &decoder circuit 3. When in a normal playback operation, the switch 112selects the memory from which data is read. As explained above, when ina normal playback operation, the data order changed when in a recordingoperation is returned to the initial order and normal MPEG bit streamsare sent to the compression encoder & decoder circuit 3. The compressionencoder & decoder circuit 3 executes normal MPEG-decoding to reproduceNTSC signals just like in the first embodiment.

Subsequently, the fast playback operation of the monitored video datarecording & playback apparatus in the fourth embodiment of the presentinvention will be explained. When a “fast playback” is instructed fromthe operator panel, the control circuit 19 sends the “NORMAL PLAYBACK”command to the VTR 9 via the I/F circuit 14. According to the command,the VTR 9 plays back data from the magnetic tape. Playback data is thensent to the second memory via the I/F circuit 14, and to the controlcircuit 19 at the same time. The control circuit 19 detects the PCT(Picture Coding Type) in the playback data to decide the playback datavideo type. When the video type is decided to be I type, the “normalplayback” operation is continued. And, the playback data is entered intothe data sorting circuit 18 via the second memory 8, the SCSI controller5, the HDD 7, and the first memory 4. The playback data entered into thedata sorting circuit 18, after the order code is deleted from itself inthe order code deletion circuit 113 just like when in a normal playbackoperation, is written into the I memory 109. Reading from this I memory109 is executed intermittently as shown in the timing chart in FIG. 14.While no data is read from the I memory 109, the memory control circuit111 generates the freeze signal. This freeze signal is sent to thecompression decoder circuit 3 via the control circuit 19. Thecompression decoder circuit 3 delays the freeze signal by a timerequired to the decoding and stops writing into the image memory 41. Atthe same time, the circuit 3 changes over the switch 44 to the output ofthe image memory 41. Consequently, compressed and decoded video data andits frozen data are output alternately. In the timing chart shown inFIG. 14, one decoded image frame is frozen twice. In this FIG. 14, it isassumed that I pictures are encoded at pitches of 15 frames. Each outputpicture is numbered. As shown in FIG. 14, after the first picture isoutput by 3 frames, the 16th picture is output by 3 frames, and then the31st picture is output by 3 frames. Consequently, the average changespeed of the output pictures becomes 15/3=5 times. In other words,pictures are output at a 5-time speed.

When such a normal playback operation is continued, the magnetic tapecomes to a region where P and B pictures are recorded. Then, the controlcircuit 19, when deciding the playback data picture type to be a P or Bpicture, sends the “600 TRACKS FAST FEED” command to the VTR 9 via theI/F circuit 14. The VTR 9 plays back the CTL signals recorded in thecontrol track of the magnetic tape and feeds the magnetic tape fast bycounting the CTL. When the CTL count value reaches 600 tracks, the VTR 9sends the “end of fast feed” information to the control circuit 19 viathe I/F circuit 14. The control circuit 19 sends the “NORMAL PLAYBACK”or “STOP” command to the VTR 9 via the I/F circuit 14 according to thedata amount in the HDD. In other words, when the data amount is less,the “NORMAL PLAYBACK” command is sent. When the data amount is much andthe HDD might overflow, the “STOP” command is sent.

As explained above, according to the fourth embodiment of the presentinvention, only I pictures can be played back and output selectively.Thus, the playback pictures can be displayed fast. Furthermore, sincethe operation mode of the VTR 9 in a playback operation of the Ipictures is normal playback, the tracing angles of the heads 81 and 82match with the angle of the recording track pattern on the magnetic tape79. This is why perfect pictures can be played back with less S/Ndegradation. In the above embodiment, since two frames of a picture arefrozen, the picture is fed at a 5-time speed. The speed can be selectedas follows. If only a frame is frozen, the picture can be fed at a10-time speed, and furthermore, the picture can be fed at a 15-time ifno frame is frozen.

As understood clearly from the above detailed explanation, according tothe apparatus and method of the present invention for recording andplaying back monitored video data, the video data to record iscompressed on the time axis, so the period of recording video databecomes shorter than the period in which video signals are generatedcontinuously. Consequently, the apparatus requires no mechanism to feedthe magnetic tape very slowly or intermittently, since a recordingoperation is not continued for a long time. It can be doneintermittently unlike the conventional method, which must continuerecording of data while the VTR must be in contact with the magnetictape while the recording head rotates. Any general home VTR can thus beused as the VTR of the present invention, reducing the costsignificantly. In addition, the apparatus can record video data for along time enough for the purpose of monitoring. And, furthermore, themethod of the present invention can suppress the degradation of themagnetic tape, the wear of the recording heads, or the degradation ofthe driving belt and other mechanical items significantly. When the timeaxis is thinned out, the rate of the operation time of the secondrecording & playback apparatus becomes lower than the monitoring andrecording time. Thus, the above effect increases further more.

In addition, according to the monitored data recording & playbackapparatus of the present invention, the VTR can record and play backdata at a normal tape feed speed, so it does not require controlling ofhigh precision intermittent tape feeding, which is indispensable for theprior art time lapse VTR. The manufacturing cost of the apparatus canthus be reduced significantly, as well as the apparatus can be free ofthe S/N degradation to be caused by mismatching of the track angle onthe magnetic tape with the tracing angle of the recording head, enablinggood quality playback pictures to be output.

Furthermore, according to the monitored data recording & playbackapparatus of the present invention, only the video data compressed andencoded at the m-frame time intervals is recorded in units of n frameson the magnetic tape, so only that portion is usually played back andother portions are fed fast, so that video data can be played back fastwith no N/S degradation to be caused by mismatching of the track angleon the magnetic tape with the tracing angle of the recording head.

1. An apparatus for recording and playing back monitored video data,which can record video data for a long time, comprising: first memorymeans for storing video data temporarily; first recording and playingback means for recording and playing back output data from said firstmemory means in a recording medium; second memory means for storingplayback data from said first recording & playback means temporarily;and second recording and playing back means for recording data outputfrom said second memory means on a magnetic tape by forming obliquetracks on said magnetic tape, controlling means for controlling theoperations of writing and reading of said first and second memory meansand recording and playback operations of said first and second recordingand playback means, said controlling means further includes the stepsof; controlling so that reading video data from said first memory meansand recording by said first recording & playback means are repeated eachtime the first specified data amount is reached in a recordingoperation, executing playback operation of said first recording &playback means and recording operation of said second recording &playback means in first operation mode so that those operations arestopped until the data recorded by said first recording & playback meansand not played back yet reaches second specified data amount which isgreater than said first specified data amount, and setting secondoperation mode so that recording and playback operations of said firstrecording & playback means are time-shared until data of said secondspecified data amount is played back completely, when said data recordedand not played back yet reaches said second specified data amount, andexecuting the recording of the data read by said second memory means ata specified transfer speed in second operation mode in which recordingby said second recording & playback means is performed while feeding themagnetic tape continuously by forming tracks obliquely on said magnetictape.
 2. An apparatus for recording & playing back monitored video data,comprising first memory means for storing video data temporarily; firstand second recording and playing back means for recording and playingback data output from said first memory means on a recording medium;second memory means for storing playback data temporarily from saidfirst and second recording & playback means; third recording and playingback means for recording and playing back data output from said secondmemory means on a magnetic tape by forming oblique tracks on saidmagnetic tape; and controlling means for controlling the operations ofwriting and reading of said first and second memory means as well asrecording and playing back of said first, second, and third means forrecording and playing back video data, said controlling means furtherincludes the steps of; selecting one of four operation modes accordingto the recorded data amount and the playback data amount in said firstand second recording & playback means, when video data is recorded, andin said first operation mode, controlling so that reading video datafrom said first memory means and recording by said first recording &playback means are repeated each time first specified data amount isreached, while recording and playback operations of said second andthird recording & playback means are stopped, and in said secondoperation mode, controlling so that reading of video data from saidfirst memory means and recording by said second recording & playbackmeans are repeated each time said first specified data amount isreached, and storing video data read from said first recording &playback means in said second memory means temporarily, thereafterreading said video data from said second memory means at a specifiedtransfer rate while enabling said third recording & playback means torecord transferred data continuously on a magnetic tape by formingtracks obliquely on said magnetic tape, and in said third operationmode, controlling so that reading of video data from said first memorymeans and recording by said second recording & playback means arerepeated each time said first data amount is reached, while recordingand playback operations of said first and third recording & playbackmeans are stopped, and in said fourth operation mode, controlling sothat reading of video data from said first memory means and recording bysaid first recording & playback means are repeated each time said firstspecified data amount is reached, and video data read from said secondrecording & playback means is stored in said second memory meanstemporarily, thereafter reading the video data from said second memorymeans at a specified transfer rate while enabling third recording &playback means to record transferred data on a magnetic tape fedcontinuously by forming tracks obliquely on said magnetic tape.